Plastic has taken the place of other materials in a variety of industries. In the packaging industry, plastic has replaced glass to minimize breakage, reduce weight, and reduce energy consumed in manufacturing and transport.
Polyethylene terephthalate (PET) is very often used as a plastic for replacement of glass in the packaging industry, particularly the beverage container industry.
U.S. Pat. No. 5,874,517 (Huang et al,) discloses the problems in the art of regenerated acetaldehyde in PET resin and their method for solving that problem.
As described in Huang et al., acetaldehyde is one of several byproducts created during PET polymerization, and remains in the polymer chip after polymerization is completed. Acetaldehyde must be minimized because it can introduce flavor to the drinks contained in the bottles, which is highly undesirable. The acetaldehyde trapped in the chip during the polycondensation reaction to prepare PET, is widely known as “free” acetaldehyde. In addition to free acetaldehyde, acetaldehyde may also be formed by the further reaction or decomposition of PET and other byproducts (“acetaldehyde precursors”) trapped in the polymer chip during polymer manufacture. Acetaldehyde produced from the reaction of trapped acetaldehyde precursors or which is formed during degradation occurring during the molding process is referred to as “regenerated” acetaldehyde. Reactions which produce regenerated acetaldehyde are induced when the polymer is subjected to high temperatures, such as those temperatures utilized in the injection molding process.
Huang et al. reports that antioxidants have been widely studied and used for preventing PET thermal and thermal oxidative degradation. But none reported by Huang et al. worked in order to reduce regenerated acetaldehyde while also maintaining color values acceptable for bottle resin.
U.S. Pat. No. 6,569,479 (Rule) discloses an oxidation catalyst active for the oxidation of acetaldehyde to acetic acid to be used in a beverage container.
U.S. Pat. No. 6,632,874 (Rule et al.) discloses decreasing aldehyde content in polyolefin materials by combining with the polyolefin material an organic additive compound which reacts with aldehydes to form water and a resulting organic compound.
U.S. Pat. No. 6,274,212 (Rule et al.) discloses a method for decreasing acetaldehyde content of melt processed polyester comprising combining with melted polyester an organic additive compound which scavenges acetaldehyde from the polyester without imparting discoloration to the polyester. The organic additive compound comprises at least two hydrogen substituted heteroatoms bonded to carbons of the organic additive compound such that the organic additive compound is reactive with acetaldehyde in the polyester to form water and a resulting organic compound comprising an unbridged five or six member ring including the at least two heteroatoms. The reduced acetaldehyde content polyester is particularly useful for making containers such as for packaging beverages.
Despite the statements in U.S. Pat. No. 6,274,212 (Rule et al.) about lack of discoloration, makers of commercial polyester beverage containers have noted yellowing of the container when following the teachings of this patent document.